Method for manufacturing an identification plate

ABSTRACT

A method of manufacture of an identification plate: comprises advancing a transparent sheet material having an opaque material in contact with one major surface thereof to a printing station, printing indicia in reverse on the other major surface of the sheet material, and securing the printed sheet material to a substrate having a retro-reflective surface such that the printed surface is in contact with, or at least adjacent to, the retro-reflective surface.

BACKGROUND OF THE INVENTION

This invention relates to identification plates and, in particular, toplates which indicate the provenance of an object to which they areattached. Such plates are conventionally termed licence or number plateswhen attached to a motor vehicle.

From 01 Sep. 2001, each United Kingdom licence plate must conform toBritish Standard BSAU 145d which governs, inter alia, the impactresistance and the minimum retro-reflectivity of the plate. Similaralthough, in some cases, less stringent provisions exist across theentire European Union, as they do in most other countries across theworld.

GB 2126386 A discloses a method of producing licence plates for avehicle, in which indicia are printed onto a carrier. The carrier may beeither a reflective surface or a plastics coating, such as a relativelythick transparent plastics sheet to provide structural support for theplate.

EP 0806752 A1 discloses an identification plate and a method ofmanufacture of such a plate wherein a rigid transparent substrate hasindicia printed thereon. The resulting printed plate is then adhered toan opaque liner such that the indicia are visible through thetransparent sheet.

It is known to print on to a nominally retro-reflective surface and thento adhere to that surface a lens, such as a clear polymer layer, toimpart to that surface a retro-reflective character. The lens may be atransparent, relatively thick, acrylic layer applied over theretro-reflective surface or a relatively thin layer with a relativelythick backing layer to provide support, as is disclosed in WO 94/19769A2.

Retro-reflective sheet material is typically a beaded substance whichhas a rough surface. Consequently, it is difficult to print on, sospecial formulations of sheet materials, which are able to ‘take’ theink, special printing materials such as ribbons, together with the useof elevated print-head temperatures are required. Both of these factorsincrease the cost. The coarse surface structure of the speciallyformulated retro-reflective sheet materials can reduce print-headoperating life and the elevated print-head temperatures can also reduceprint-head lifetimes. It has also been found that print quality suffersat elevated print-head temperatures and with such rough surfaces.

SUMMARY OF THE INVENTION

It is an object of this invention to provide identification plates whichcan be manufactured by either a continuous process or as an individualplate. It is a more specific object to provide methods of manufacturewhich are simpler than prior art methods, enabling more efficientassembly of the necessary components and which have reduced the costscompared with known methods. It is a further object of the invention toprovide methods of manufacture which provide a manufacturer with agreater degree of flexibility in production, allowing bespoke or“multi-run” plates to be produced.

According to a first aspect of the invention there is provided a methodof manufacture of an identification plate, the method comprising:

-   -   advancing a transparent sheet material having an opaque material        in contact with a first major surface thereof to a printing        station;    -   printing indicia in reverse on to a second major surface of the        sheet material;    -   securing the printed sheet material to a substrate having a        retro-reflective surface such that the printed surface is in        contact with, or at least adjacent to, the retro-reflective        surface.

A more specific aspect of the invention provides a method ofmanufacturing an identification plate, the method comprising:

-   -   advancing a substrate-sized length of transparent sheet material        to a printing station, the sheet material having an opaque        substance in contact with one major surface thereof;    -   optically sensing passage of the leading edge of the        substrate-sized length of transparent sheet material by        attenuation of an optical beam by the opaque substance;    -   printing indicia in reverse on the other major surface of the        sheet material;    -   securing the printed transparent sheet material to a substrate        having a retro-reflective surface such that the printed surface        is in contact with, or at least adjacent to, the        retro-reflective surface; and    -   removing the opaque material from the transparent sheet        material.

A further aspect of the invention provides an identification platecomprising a supporting substrate having two opposed major surfaces, theentire first major surface being retro-reflective, a transparent sheetmaterial having indicia printed thereon, the transparent sheet materialbeing adhered to the first major surface such that the indicia arelocated adjacent the first major surface.

There is further provided, by a fourth aspect of the invention, anidentification plate comprising a supporting substrate having aretro-reflective major surface and an transparent sheet material anentire major surface of which having marking material applied thereto,the transparent sheet material being adhered to the retro-reflectivemajor surface such that the marking material is in contact with, or atleast adjacent to, the retro-reflective major surface.

A fifth aspect of the invention provides a method of manufacture of anidentification plate, the method comprising:

-   -   conveying a transparent sheet material toward printing means;    -   optically sensing the passage of the transparent sheet material        as it is conveyed toward said printing means;    -   actuating printing means in response to said passage of the        transparent sheet to print indicia in reverse on the other major        surface of the sheet material; and    -   securing the printed sheet material to a substrate having a        retro-reflective surface such that the printed surface is in        contact with, or at least adjacent to, the retro-reflective        surface.

In a fourth aspect of the invention, there is provided an identificationplate comprising a laminate of a support and a transparent sheetmaterial having indicia printed on a surface thereof, the supportcomprising a matrix material in which is retained a plurality ofreflective particles, wherein the indicia are in contact with or are atleast adjacent to a major surface of the support and the transparentsheet material provides a lens for the reflective particles located atthat major surface, thereby providing the plate with a retro-reflectivecharacter.

A further aspect of the invention provides a method of manufacture foran identification plate, the method comprising the steps of:

-   -   providing a support having reflective particles distributed in a        matrix, wherein the particles are at least present at a first        surface of the support;    -   printing indicia, in reverse, on a surface of a transparent        sheet material;    -   adhering the sheet material to the first surface of the support        so that the indicia are sandwiched therebetween;

whereby the sheet material acts as a lens for the particles, imparting aretro-reflective character to the plate.

The reflective particles may be uniformly distributed throughout thesupport or may be uniformly and/or preferentially distributed at ortowards the surface thereof.

The support may be formed by moulding a substance having reflectiveparticles therein. The support may be formed by laminating aretro-reflective sheet material to a substrate. The support may have anextension portion, for example an elongate lip. The support may compriseone or more frangible portions.

Techniques are known for preferentially distributing particles at asurface of a moulded article. Such techniques include gravity separationwhilst the matrix material is in a fluid state, which may rely on adifference in density between fluid matrix material and the particles,or preferential drying of one or another surface of the mould bymicrowave energy or other means.

The reflective particles may be formed of glass, for example glass beadsor spheres, or they may be formed from a mineral or a plastics material.

The support may be formed from a plastics material, for exampleacrylonitrile butadiene styrene (ABS), polyethylene, Nylon (RTM) orother hard-wearing, impact and/or bend resistance plastics materials. Insome embodiments the substrate may be formed from a metal or an alloy,for example aluminium or steel.

Preferably, the transparent sheet material is a polymer which,advantageously, may be polyvinyl chloride, polyester, polypropylene orthe like.

Preferably, the plate has a main body for primary indicia. An extendedportion for further indicia may be provided. The extended portion may bealong one of the longer sides of the plate.

Suitable retro-reflective sheet materials are either coated ornon-coated. In such coated sheet materials, a thin acrylic layer isapplied to the beaded surface, thereby providing those reflectiveparticles with a lens and imbuing the sheet material withretro-reflective characteristics. In non-coated retro-reflective sheetmaterials the surface is only provided with a retro-reflective characteronce a lens has been applied to it. With such non-coatedretro-reflective sheet materials, when used in the methods disclosedabove, the lens is provided by the transparent material and it is onlyonce this material has been applied to the retro-reflective materialthat the whole ‘sandwich’ acts retro-reflectively. Whilst non-coatedretro-reflective materials are typically less expensive than the coatedones and for that reason may be preferred, it is possible to use eitherin the methods disclosed herein.

The transparent sheet material may be supplied on a roll, or asindividual substrate-sized lengths. If the transparent sheet material issupplied on a roll, it may be shaped as a repeating pattern, each repeatthereof corresponding to a substrate-sized length.

The opaque material may be a release sheet, in one embodiment a paperrelease sheet. Alternatively, the opaque material may be a plasticsrelease sheet, such as a polypropylene sheet. The release sheet may beprovided with a pressure sensitive emulsion adhesive layer, thetransparent material may have a silicone layer applied thereto, thesilicone layer which is contacted by the adhesive layer of the releasesheet facilitates separation of the release sheet and sheet material.The silicone layer and adhesive layer allow the release sheet and sheetmaterial two to be releasably adhered, such that the release sheet maybe re-applied to the transparent material.

Said printing means may be arranged to print over some, most, or all ofthe transparent sheet material.

The transparent sheet material may have secondary and/or otherinformation printed on the other major surface prior to being advancedto the printing station. The printing, on the transparent sheetmaterial, of any secondary and/or other information may be completed‘off-line’, which is to say that information may be printed and thetransparent sheet material stored or held for future use. The printingof secondary and/or other indicia may be completed immediately before orafter printing of the primary indicia.

Said printing means may preferably comprise a thermal mass transferprinter or an ink jet printer.

A further aspect of the invention provides a medium to bear indicia foruse in an identification plate, the medium comprising a transparentplastics film carrying a silicone material on a first major face thereofand an opaque liner carrying a pressure sensitive adhesive on a majorface thereof; a second major face of the transparent plastics film beingprintable to, wherein the silicone layer and adhesive layer are incontact and the opaque liner and transparent film are separable andre-attachable by virtue of the releasable interaction between siliconelayer and adhesive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully understood, it will now bedescribed, by way of example only, and with reference to theaccompanying drawings, in which:

FIG. 1 shows a schematic representation of a method according to theinvention;

FIG. 2 shows a schematic representation of a variant method according tothe invention;

FIG. 3 shows a section through a printable medium according to theinvention;

FIG. 4 shows a detail of part of the method described in accordance withFIG. 2;

FIG. 5 shows a section through an identification plate made inaccordance with the invention;

FIG. 6 shows section through a further identification plate made inaccordance with the invention;

FIG. 7 shows an elevation of an identification plate made in accordancewith the invention;

FIG. 8 shows an elevation of a further identification plate made inaccordance with the invention;

FIG. 9 shows a detail of a printer;

FIG. 10 shows an elevation of a yet further identification plate made inaccordance with the invention;

FIG. 11 shows a section through the plate of FIG. 8;

FIG. 12 shows an elevation of the plate of FIG. 8 from the reverse side;

FIG. 13 shows an elevation of the plate of FIG. 8 subsequent to use; and

FIG. 14 shows a variation of the apparatus of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring firstly to FIG. 1, a length of medium 1 to be printed uponcomprising a length of transparent film 2, having an opaque releaseliner 3 in contact with one major surface thereof, is advanced in thedirection of arrow A. Among other advantages, which will becomeapparent, the release liner 3 provides the length of film 2 with somerigidity, making it easier to handle. The transparent film 2 ispreferably polyester film with a thickness of about 70 μm. The opaquerelease liner 3 is preferably paper or polypropylene with a thickness ofabout 80 μm.

FIG. 3 shows a cross-section of the medium 1. The release liner 3 has apressure sensitive adhesive emulsion layer 3 a applied thereto, thatlayer is typically 10 to 15 μm thick. The transparent polyester film 2has a layer of silicone 2 a applied thereto, which is typically about 3to 5 μm thick. The silicone layer 2 a is in contact with the adhesivelayer 3 a. The silicone layer 2 a prevents complete adhesion between theadhesive layer 3 a and transparent film 2, and allows the release liner3 to be removed and reapplied to the transparent film 2. This allowsinspection of the completed plate and re-application of the releaseliner 3 to protect the surface during transit to a point of use orstorage.

The printable medium 1 is brought to a printer 5 which is a thermaltransfer printer having a printing head 6 and a ribbon 7. Mounted eitherexternally or internally of the printer 5 is an optical sensing device8, comprising an optical beam generator 9 and a detector 10, located onopposite sides of the path of travel of the medium 1.

The output of the optical beam generator 9 is detected by the detector10 in the usual way so that any non-optically transparent medium whichinterrupts the beam causes a reduction in the signal detected by thedetector 10. The signal detected by the detector 10 can be used tocontrol operation of the printing head 6. For example, if the detectedsignal rapidly decreases, due to attenuation of the beam, the reductionis detected by signal processing means 11, such as a computer, which, inturn, controls the printing head 6 to print on the film 2. Clearly, thespeed at which the medium 1 is conveyed should be monitored and/orcontrolled. Monitoring the time between maximum signals and the speed atwhich the medium 1 is conveyed allows accurate control of the locationof so-printed indicia.

As the printable medium 1 passes through the optical beam, the signaldetected by the detector 10 reduces, due to the presence of the opaquerelease liner 3. The signal processing means 11 responds to thereduction of detected signal to control the printing head 6 to start andfinish printing the desired indicia on the transparent film 2, inreverse. That is to say that the printer 5 prints on the underside, asshown in FIG. 1, of the transparent film 2. The opaque liner 3, whichhas a rougher surface than the transparent sheet material 2 and addsextra effective thickness, enables the rollers of the printer to bothgrip the medium 1 and keep it in accurate registration and thereby printonto the transparent film 2.

A computer, which may or may not be the same as said signal processingmeans 11, holds a store of the indicia desired to be printed onto themedium 1. The information is transmitted to the printer 5 whichpreferably arranges the formatting of the desired indicia. An eminentlysuitable and preferred printer is a QLS-4100 series, supplied byAstro-med Incorporated of Rhode Island, USA. The print rate of such aprinter can be as high as 20.4 cm per second, but is more typicallyoperated at 7.6 cm per second. Therefore, using such a printer withoptical control, up to 1200 standard British vehicle licence plates(52.1×11.1 cm) per hour can be produced automatically.

The resulting printed medium 15 is advanced to a lamination station 17.A length of substrate 20 moulded from ABS with a retro-reflectivesurface 22 is also advanced to the lamination station 17. The substrate20 is typically from 2.5 to 3.8 mm thick, preferably 3.2 mm thick. Thesubstrate has a release sheet 23 covering a pressure-sensitive adhesivelayer (not shown). The adhesive layer has been previously applied, i.e.off-line, although it may be applied as part of the process. The releasesheet 23 is removed as the substrate 20 is advanced to the laminationstation 17.

The printed medium 15, comprising transparent film 2 and opaque releaseliner 3, and the length of substrate 20 are shown as being rectangular,with right-angle corners. Other shaped corners are possible, forexample, each of the components 2, 3, 20 may have curved or radiusedcorners.

The so-formed laminated composite 30 is advanced to a further pointwhere the opaque releasable liner 3 is removed from the transparent film2, thereby providing a finished identification plate 40. Removal of therelease liner 3 may be carried out prior to or subsequent toinstallation of the plate 30 on a vehicle so that the surface of theplate 30 is protected during transit. The silicone layer 2 a will beremoved by the action of the elements, precipitation, wind and so on.

The transparent film 2 acts as a lens for a non-coated retro-reflectivesurface 22 providing it with a retro-reflective characteristic. As thelens for the retro-reflective surface 22 is simply a thin film 2 ratherthan a thick, transparent substrate, as is the case in certain prior arttechniques, it is found that the indicia are clearer and the plate 40has a higher retro-reflectivity (due to the much shorter path length forimpinging and reflected light), both of which are desiderata of vehiclelicence plates. When coated retro-reflective surfaces 22 are utilised,the thin film 2 does not impair the retro-reflective character of thesurface 22.

The above description has concentrated on what may be called individualor ‘single-shot’ printing. However, what may be termed continuous,‘batch’ or web printing may also be used, wherein a length of printablemedium 1′ comprising a web of transparent film 2 provided with areleasable backing layer 3 is delineated into substrate-sized lengths bytransverse perforations 4, as shown in FIG. 4. The individual lengthsare shaped with rounded corners 18.

Referring to FIGS. 2 and 4, the printable medium 1′ (in FIG. 2) is shownas an individual length for the sake of clarity but, as will beappreciated, the medium 1′ is a continuous length or web. The medium 1′is advanced to the printer 5, as indicated by arrow A. As a lengthpasses over the optical beam generator 9, the detected signal reaches amaximum when a ‘viewing window’ 12, formed by the rounded corners 18 ofadjacent individual lengths of printable medium 1′, is directly in thepath of the optical beam. The maximum detected signal will correspond towhen the least amount of beam-attenuating material lies between the beamgenerator 9 and detector 10, such as when the perforations 4 are in-linewith the optical beam. The minimum detected signal occurs when the mostbeam-attenuating material lies between the beam generator 9 and detector10. Both extremes are shown in FIG. 2. By pre-calibration, thedifference between maximum and minimum signals can be used to controlthe printing head 6 to print indicia, in reverse, on a major surface ofthe transparent film 2.

The resulting printed medium 15′ has an adhesive applied to itslowermost surface, i.e. the surface which was printed on to, at adhesiveapplication station 16. A release liner may then be applied to thatsurface to protect the adhesive from contamination atrelease-liner-application station 19 a.

The further release liner-carrying printed medium 15′ is advanced to alamination station 17. A length of substrate 20 moulded from ABS, with aretro-reflective surface 22 is similarly brought to the laminationstation 17. The substrate 20 is typically from 2.5 to 3.8 mm thick,preferably 3.2 mm thick.

Immediately prior to registration of the printed medium 15′ with thesubstrate 20, the further release liner, if previously applied, isremoved from the adhesive-bearing surface of the printed medium atrelease-liner-removal station 19 b. The printed medium 15′ and substrate20 are laminated together, using pressure, as indicated by arrows B inthe station 17, thereby sandwiching the indicia between theretro-reflective surface 22 and the transparent film 2. The adhesive ispressure-sensitive, which is to say it acts to adhere the two components15′, 20 through the application of pressure. A suitable acrylic adhesiveis S2001, supplied by MACtac Europe SA. The release liner may havetransverse perforations corresponding to those 4 of the medium 1′.

The leading edge of the first printed length is brought into intimatecontact with a length of substrate 20, having a retro-reflective surface22. Either before or after lamination of the printed length to thesubstrate 20 has been fully effected, the perforations are broken toprovide a separate identification plate 40.

In an alternative arrangement, the medium 1′, having a shapedtransparent film 2 with correspondingly shaped opaque release liner 3 asbefore, is not delineated by transverse perforations 4, the line 4 beingthe intended location of a cut line or perforated line about whichindividual lengths will be provided. The printer 5 is actuated followingoptical monitoring of the passage of the medium 1′ passed an opticalsensing device 8, as above. An adhesive is applied to the printedsurface of the transparent film 2 which then has a further release linerapplied thereto to protect the adhesive from contamination.

The so-formed medium 15′ may be cut into substrate-sized lengths atintended cut line 4 prior to removal of the further release liner atstation 19 b or subsequent to removal of that further release liner atstation 19 b, the latter being the most preferred.

The substrate 20 may be formed in many ways. The first is simply tomould or extrude ABS or to cut a substrate to the desired shape and sizefrom a sheet of material and adhere, by lamination, a retro-reflectivefilm to one major surface thereof. Suitable retro-reflective filmmaterials are Diamond Grade and Engineer Grade retro-reflective sheetingsupplied by Minnesota, Mining and Manufacturing Company (3M) of St.Pauls, Minn., USA, although others may be used. It is often beneficialto mould the surface of the substrate 20 with a slightly textured orroughened surface to aid adhesion of the retro-reflective materialthereto.

Other retro-reflective sheet materials which may be used are formed as acomposite of a retro-reflective sheet material having an adhesiveapplied to both major surfaces thereof, the adhesive being covered byrelease sheets. The intended lowermost surface of the retro-reflectivesheet material is adhered to a suitably sized length of substrate bylamination following removal of the lowermost release sheet. Thesubstrate, with retro-reflective sheet material applied thereto, canthen be stored for subsequent use or can be used immediately by removingthe uppermost release sheet, thereby exposing the adhesive-coveredretro-reflective surface. The printed upon surface of the transparentsheet is then laminated thereto. Such a retro-reflective compositeobviates the need for an adhesive application station 16 or to applyadhesive to the retro-reflective surface.

As one alternative, the ABS, or other plastics material from which thesubstrate 20 is moulded, has a substrate-sized length ofretro-reflective material moulded therewith.

To effect such moulding, the leading edge of a length ofretro-reflective sheet material is placed, pulled or otherwise drawninto a mould, where it is clamped in place. One portion of the mouldthen closes on the sheet. Whilst one major surface of theretro-reflective material is in contact with the top of the mould, acavity is provided between the other major surface of theretro-reflective material and the bottom of the mould. A plasticsmaterial, such as ABS, is injected into the cavity. As the mould isclosed shut, the retro-reflective material is adhered to the substrate20. The length of retro-reflective material may be the same size as themould or it may be over-sized. If it is over-sized the excess will betrimmed off.

Such a method removes the need for forming a substrate length 20 with aroughened surface and subsequently laminating a retro-reflective sheetmaterial thereto, thereby reducing the cost.

Referring to FIG. 5, a sectional view of a plate 40 made according tothe above-described method is shown. The substrate 20 is a mouldedlength of plastics material, such as ABS, which has a plurality ofreflective glass beads 21 retained therein which provide theretro-reflective surface 22. Adhered to the substrate 20 is atransparent plastics film 2, having indicia 43 printed thereon.

The substrate 20 shown in FIG. 5, is formed by moulding a plasticsmaterial in which is distributed reflective bodies, such as glassspheres of, say, up to 15 μm diameter. Once the plastics material isforced into the mould, the glass spheres are allowed to settle bygravity (if their density is greater than that of the fluid plasticsmaterial) or rise to the surface (if their density is less than that ofthe fluid plastics material). As an alternative, selective drying bymicrowaves can be used to encourage the beads 21 to preferentially movetoward one surface. Other methods for achieving such a result are knownto the man skilled in the art.

FIG. 6 shows a plate 40′ having a substrate 20′, to which is attached afilm 2 having indicia 43 printed thereon. In this substrate 20′, thereflective particles 21 are substantially evenly distributed throughoutits' thickness. The number of particles 21 per unit volume may begreater than as shown to achieve the necessary retro-reflectivity of thecompleted plate 50.

In this case, the particles 21 are not allowed to settle or rise to asurface. Alternatively, the concentration of particles 21 within theplastics material 20′ may be so great that they are unable topreferentially settle toward a particular surface or they may have adensity substantially equivalent to that of the fluid plastics material,thereby preventing any preferential settling of one component over theother.

Once the transparent plastics film 2 has been applied to the surface ofthe substrate 20, 20′ it has a retro-reflective character. Whilst glassbeads and other reflective particles do not have as high an absolutereflective property as bespoke retro-reflective materials, because thefilm 2 is so thin, compared to a lens using a 3.2 mm thick acrylatesheet (as is considered in certain prior art applications), theretro-reflectivity of the plates 40, 40′ is sufficient to meet therequired standard.

FIG. 7 shows an identification plate 40 a, which can be fabricated usingthe above-described methods. The plate 40 a has a main body portion 44with visible indicia 43.

FIG. 8 shows a plate 40 b with an extended portion 41 along the intendedbottom edge thereof for tertiary indicia 42. Primary indicia 43 arevisible. Secondary indicia (not shown) may be printed on the transparentfilm 2 to stand out against the main body 44′ of the plate 40 b. Thetertiary indicia 42 may comprise advertising or other personalisationsand may be printed “off-line” or may be printed concurrently with, orconsecutively to, the primary indicia 43. A white or other colouredbacking layer may be applied to the substrate 20 over the extendedportion 41 to provide a backing for the tertiary indicia 42. In afurther embodiment, the tertiary indicia 42 may be printed in a colourwhich is visible against the substrate 20. The transparent film 2 may beapplied to the whole, part or none of the extended portion 41. Theretro-reflective surface 22 may extend over some or all of the extendedportion 41.

Clearly, with computer control of the printer 5, different indicia canbe printed on subsequent lengths of media 1, 1′. In the case of vehiclelicence plates, it is possible to print two identical sets of indicia onsubsequent lengths, one for the front and one for the rear plate, andthen to print another two identical sets of indicia, and so on.

The printable media 1, 1′ may be pre-printed with general information assecondary indicia. Such information may show the manufacturer, supplieror other personalisations, security information and the like. Suchpre-printing provides a greater degree of flexibility for a manufacturerwith a small turnover of identification plates as any generalinformation is pre-printed and the printer 5 can be used to simply printthe desired specific, primary indicia 43, such as a licence platenumber. Thus, a manufacturer can hold supplies of the pre-printedprintable medium 1, 1′ and print primary indicia 43 as and whenidentification plates 40 are required.

Using process control printing, as is possible with the Astro-med QLS4100 series printer, it is possible to simplify further, andcommensurately reduce the cost of, fabricating a licence plate.

One of the requirements of the British Standard referred to above isthat the retro-reflective material of the vehicle's intended rear numberplate is a certain shade of yellow. In Greece, for example, one of thebackground colours of the plates must be blue. It is a furtherrequirement, within Europe, that a regional country identifier as wellas the Euro flag (EU Council Regulation 2411/98[3]) is provided on acar's licence plate when travelling from a ‘home’ country to a differentEuropean country. Because, conventionally, the country identifier issupplied printed on to the retro-reflective sheet material the costs areincreased. Furthermore, yellow and other coloured retro-reflectivematerials which meet the required standards are relatively expensive.

Using process control of the printer 5, it is possible to print atranslucent coloured marking material onto the transparent film 2.Further, it is possible to print a blue ‘Euro’ flag on to thetransparent film 2 and the country identifier as well as the primaryindicia 43 and any secondary and any tertiary indicia 42. The printer 5prints each of the primary 43, secondary and any tertiary indicia 42, aswell as the coloured translucent material on to the transparent film 2from dedicated printing ribbons 7. None of any of the respective markingmaterials need overlay any other, due to accurate and precise computercontrol of the print head 6.

Clearly if, as in the United Kingdom, the intended rear (yellow) andfront (white) vehicle number plates are different colours, twomanufacturing lines will conventionally be used. An alternative is toalternate the coloured plates say, yellow and white, on a manufacturingline. This approach can lead to problems when one of a pair of platesis, say, spoiled or if, say, two white or two yellow coloured substratesare placed on the manufacturing line by mistake. Thus, by processcontrol printing, stock levels can be reduced as can the number ofmanufacturing lines needed.

The coloured translucent material applied to the film 2 allows a whiteretro-reflective surface 22 to be used, the coloured translucent markingmaterial imbuing the so-formed plate with the required colour. Suchwhite retro-reflective sheet materials are significantly cheaper thanthose in the required shades of yellow and other colours. The thicknessof the coloured marking material applied to the film 2 is such that itonly minimally interferes with the retro-reflective nature of theretro-reflective material. Such an approach may also be used to providethe required colour of retro-reflective surface of the plates 40, 40′ ofFIGS. 3 and 4.

FIG. 9 shows a detail of the printer 5, having the thermal printing head6 and ribbon 7′. As the printable medium 1, 1′, having a transparentsheet 2 and release liner 3, passes over the ribbon 7′, the printinghead 6 is activated to transfer some of the pigmented wax and/or resinon the ribbon 7′ to the transparent sheet 3 through the application ofheat and pressure.

Certain colours, such a black and red tend to be laid onto thetransparent film 2 such that the retro-reflective surface 22 is notvisible through those indicia. For those colours, a conventional singlelayer ribbon 7 wherein a single layer of wax and/or resin colouredmarking material is provided on a foil and is transferred to the film 2by the application of heat and pressure from the print head 6.

However, in some circumstances, and with some colours, it is necessaryto ensure that the so-printed indicia are of sufficient clarity andvisibility when the transparent sheet 3 is adhered to theretro-reflective surface 22. In those circumstances a composite ribbon7′ is provided.

The composite ribbon 7′ comprises a dual layer of wax and or resin, thefirst 72, which is intended for contact with the transparent sheetmaterial 2 is the desired colour and the second 71, which is to lieadjacent the retro-reflective surface 22 of the substrate 20 in thecompleted plate 40, 40′ is opaque, usually white. Using single layer aswell as composite ribbons 7′ ensures that the printed primary, anysecondary and/or any tertiary indicia 42, 43 are visible and alsoensures that the retro-reflective surface 22 underneath the indicia 42,43 does not show through during use.

A further advantage of moulding the substrate 20, 20′ is that it can beformed with a cavity in its' rear surface. The cavity can be sized andformed such that an electrical device can be housed therein. Suchdevices may be sensors, signal emitters or transponders. An example maybe a transponder used for traffic monitoring across a road network, forexample, across automatically charged toll roads. Alternatively, avehicle security device may be mounted therein, to warn of, say, theftof the number plates of a vehicle. A host of devices may be housed insuch a cavity. In prior art plates, where a clear substrate is appliedover the retro-reflective material, the indicia being sandwichedtherebetween, it is not possible to provide such a cavity as any deviceinstalled in such a cavity would obscure part of the retro-reflectivematerial.

FIG. 10 shows a specific embodiment of a licence plate 100 made inaccordance with the methods described above. The licence plate 100bearing indicia 43 is constructed to be tamper evident and has a firstportion 102 located between two second portions 103. No cleardelineation of the portions 102, 103 is visible from the front of theplate 100, as shown in FIG. 10.

FIG. 11 is a side elevation of the plate 100. The plate 100 is formedfrom an elongate ABS substrate 20 having opposed first and second faces106, 107.

The first face 106 is retro-reflective, either having a retro-reflectivesheet material adhered thereto or having retro-reflective particlesembedded therein. A translucent sheet material 2 having indicia 43printed thereon is adhered to the retro-reflective surface 106.

The substrate 20 has lines of weakness 110 formed in the second face107. These take the form of channels or grooves cut into or moulded withthe substrate 20.

As shown in FIG. 12, lines 110 extend across the width of the secondface 107.

Adhered to the face 107 are sticky pads 111, each being covered by arelease layer as is known in the art. A pad 111 is present on each sideof the lines 110. The pads do not extend the full width of the face 107.

To fit the plate 100 to a vehicle, the release layer is removed fromeach sticky pad 111 and the plate pressed onto the vehicle. The padscomprise a contact adhesive which adheres the plate 100 to the vehicle.

If the substrate 20 is moulded, the lines 100 are formed during part ofthe moulding process. As one alternative, the lines 100 could be milledout from the substrate 20.

A thief or other unscrupulous person who attempts to remove the plate100 from a vehicle will need to prise the plate 100 away from thevehicle. The easiest point of attack is at either end of the plate 100.The force required to remove the sticky pads 111 from the vehicle bumperis substantial, whereas the force required to snap the plate 100 about aline of weakness 110 is less. Accordingly, as an attempt is made toprise the plate 100 from the vehicle, the plate will fracture about aline of weakness 110. Once a fracture occurs, delamination of the film 2adjacent the fracture line occurs, ruining the appearance of the plate100 and ensuring that the plate 100 cannot be used again, as indicatedin FIG. 13.

Further, should a person attempt to remove the film 2 with the indicia43 from the plate 100, the strength of the adhesion of the film 2 tosurface 106 of the plate 100 causes the film 2 to stretch as it isremoved, thereby ruining the appearance of the indicia 43 and film 2.

As a further embellishment, an electric contact can be made across theline of weakness 110, so that upon an attempt to remove the plate 100from a vehicle the contact is broken and an alarm sounds. The contactmay be directly wired to the vehicles on-board alarm system.

The plate 100 appears from the front as a ‘normal’ licence plate, thusthe unsuspecting vehicle licence plate thief will not know until suchtimes as the plate 100 breaks in his hands that he cannot remove itintact.

Vehicles which would benefit from having secure, un-stealable, or tamperevident, licence plates are those for the military, police, diplomaticservice, security vans and the like. However, clearly any vehicle couldbenefit from such tamper evident plates 100.

In the above-described methods a thermal transfer printer is used, FIG.14 shows an ink jet printer 5′ having an ink jet head 67 with a UVcuring lamp 66 to dry to so-applied ink, which could be used in place ofthe thermal transfer printer. A further release layer applicationstation may be present subsequent to application of the adhesive atstation 16.

Other variations and modifications to the apparatus may be made withoutdeparting from the scope of the invention. For example, the signalprocessing means 11 may be used to control each stage of the method,conveying, printing, lamination, separation of perforations and so on.The optical beam generator and detector system may be a duplex systemwherein the output of the beam is constantly monitored by a furtherdetector, the signal utilised by the processing means 11 being a ratioof the two detected signals, thereby normalising for beam strengthfluctuation. The optical beam generator may be a simple light sourcesuch as a small bulb held in a tube, a diode or any other radiationsource which would be suitably attenuated by the release liner 3. Theadhesive which is used to ensure lamination of the printed medium 15 andthe substrate 20 may be applied to the retro-reflective surface 22 ofthe substrate 20.

The methods disclosed herein can be used to manufacture vehicle licenceplates as well as other signage—warning signs, direction signs, room-useindicators and so on. Frangible portions may be used to ensure that anysuch signs may not be removed from their intended location without themfracturing or otherwise becoming obviously removed.

1. A method of manufacture of an identification plate, the methodcomprising: advancing a relatively thin transparent sheet materialhaving an opaque release liner in contact with a first major surfacethereof to a printing station; printing indicia in reverse on to asecond major surface of the sheet material; securing the printed sheetmaterial to a relatively thick substrate having a retro-reflectivesurface such that the printed surface is in contact with, or at leastadjacent to, the retro-reflective surface and; removing the opaquerelease liner from the relatively thin transparent sheet materialsubsequent to securing the relatively thin transparent sheet to therelatively thick substrate.
 2. A method according to claim 1 furthercomprising the steps of: optically sensing passage of the leading edgeof the relatively thin transparent sheet material as it advances towardthe printing station by attenuation of an optical beam by the opaquerelease liner.
 3. A method according to claim 1, comprising thepreliminary step of securing a retro-reflective sheet material to amajor surface of the relatively thick substrate and thereby forming theentire retro-reflective surface.
 4. A method according to claim 1,comprising the preliminary step of locating a retro-reflective sheetmaterial within a mould and injecting plastics material into the mould,thereby forming a relatively thick substrate with an entireretro-reflective surface.
 5. A method according to claim 1, comprisingthe preliminary step of locating reflective particles in a moltenplastics material to form a plastics matrix and moulding that matrix toform a substrate having an entire retro-reflective surface.
 6. A methodaccording to claim 1, comprising printing, at the printing station, overthe entire major surface of the transparent sheet material.
 7. A methodaccording to claim 1, comprising pre-printing some markings on the to-beprinted upon major surface of the relatively thin transparent sheetmaterial.
 8. A method according to claim 1, comprising printing, at theprinting station, in different colours and shades over distinct portionsof the to-be printed upon major surface of the relatively thintransparent sheet material.
 9. A method according to claim 1, comprisingsupplying the relatively thin transparent sheet material from a roll ofrelatively thin transparent sheet material.
 10. A method according toclaim 9, wherein the roll of relatively thin transparent sheet materialis shaped to have a repeating pattern, each repeat being asubstrate-sized length.
 11. A method according to claim 1, comprisingsupplying the relatively thin transparent sheet material as individualsubstrate-sized lengths.
 12. The method according to claim 1, furthercomprising forming one or more lines of weakness in the relatively thicksubstrate.
 13. The method according to claim 1, further comprisingforming a cavity in the relatively thick substrate for a location of anelectronic or electric device.
 14. A method of manufacture of a vehicleidentification plate, the method comprising: conveying a relatively thintransparent sheet material toward printing means said transparent sheetmaterial having an opaque release liner in contact with a first majorsurface thereof; optically sensing the passage of the relatively thintransparent sheet as it is conveyed toward said printing means;actuating printing means in response to said passage of the relativelythin transparent sheet material to print indicia in reverse on a secondmajor surface of the relatively thin transparent sheet material; andsecuring the printed relatively thin transparent sheet material to arelatively thick substrate having an entire retro-reflective surfacesuch that the printed second major surface is in contact with, or atleast adjacent to, the entire retro-reflective surface, and subsequentlyremoving said opaque release liner.
 15. A method according to claim 14,comprising the preliminary step of securing a retro-reflective sheetmaterial to a major surface of the relatively thick substrate andthereby forming the entire retro-reflective surface.
 16. A methodaccording to claim 14, comprising the preliminary step of locating aretro-reflective sheet material within a mould and injecting plasticsmaterial into the mould, thereby forming a relatively thick substratewith an entire retro-reflective surface.